The document discusses principles of visual perception and information visualization design. It describes how early visual processing works in the brain's primary visual cortex (V1), including how V1 analyzes basic visual features like orientation, color and motion. It explains that V1 provides input to the "what" and "where" pathways, which are involved in object identification and spatial awareness. Principles of pre-attentive processing and visual search strategies are covered, noting how some visual features like color or size differences "pop out". Guidelines are provided for design to leverage these principles to make certain information easily visually distinct and searchable.

1. Visual Thinking and
Information Visualization Design
10/11 Week4

2. p.23

3. This chapter is about
• the theory of vision that describes what makes something small
easy to see.
• nitty-gritty details of design.
p.23

4. The perceptual laws of visual distinctness are based on
• low-level early-stage processing in the visual systems.
all graphical interpretation is built on
• the elementary pattern-processing systems we find there provide the
substrate
p.24

5. Is there a “p”? Is there a “q”?
The fact that p’s are easy to see seems straightforward
and unsurprising. But why do the q’s take longer to find?
p.24

6. The Machinery of Low-level Feature Analysis
At the back of the brain in a region called the primary visual cortex (also called
visual area 1, or V1) cells would “fire,” thereby emitting a series of spikes of
electrical current when certain kinds of patterns were put in front of an animal’s eye.
• V1 is a kind of tapestry of interlocking regions where different kinds of
information are processed.
• Visual area 2 (V2) receives input from V1. V2’s neurons respond to slightly more
complex patterns, based on the processing already done in V1.
p.25

7. These cortical areas are parallel computers because they process every part of
the visual image simultaneously, computing local orientation, local color size
information, and local motion information.
p.25

8. What and Where Pathways
V1 and V2 provide the inputs to two distinct processing systems called the
what and the where systems, respectively.
p.26

9. • The what pathway - identification of objects in the environment.
• The where pathway - location of information and guiding actions in the world.
p.26

10. Eye Movement Planning
Biased competition
• If we are looking for tomatoes, what instruction can be issued?
• red-sensitive cells in V1 > shout louder
• blue- and green-sensitive cells > quiet
• Similar to orientations, or sizes—these are all features processed by
V1.
• The responses from the cells that are thereby sensitized are passed
both up the where pathway, to regions that send signals to make eye
movements occur.
p.26-27

11. What stands out = What We Can Bias For
p.27

12. p.27

13. Pre-attentive occurred because of automatic mechanisms operating prior to
the action of attention and taking and taking advantage of the parallel
computing of features that occurs in V1 and V2.
p.28

14. Pre-attentive
• Intense concentrated attention is required for the kinds of experiments
Triesman carried out.
• Recent experiments where subjects were not told of target ahead of time
show that all except the most blatant targets are missed. This is why pre-
attentive is a misnomer
p.29

15. A better term would be tunable, to indicate those visual properties that can be
used in the planning of the next eye movement.
The strongest pop-out effects occur when a single target object differs in some
feature from all other objects and where all the other objects are identical, or at
least very similar to one another.
p.29

16. Visual distinctness has as much to do with the visual characteristics of the
environment of an object as the characteristics of the object itself.
The simple features that lead to pop out are
• color
• orientation,
• size
• motion
• stereoscopic depth
Exception
• Convexity
• Concavity
p.29

17. p.30

18. p.30

19. p.30

20. p.30

21. Conjunction Search
Trying to find a target based on two features is called a visual conjunctive
search, and most visual conjunctions are hard to see. The easy-to-find
things can be differentiated by neurons farther up the what pathway.
p.30

22. For the pop-out effect to occur, it is not enough that low-level feature
differences simply exist, they must also be sufficiently large. The more the
background varies in a particular feature channel—such as color, texture, or
orientation—then the larger the difference required to make a feature distinct.
p.31

23. Feature Channels
• Channels are defined by the different ways the visual image is processed
in the primary visual cortex.
p.32

24. One might think that finding things quickly is simply a matter of practice
and we could learn to find complex patterns rapidly if we practiced
enough. The fact is that learning does not help much.
p.32

25. Lesson For Design
If you want to make something easy to find, make it different from its
surroundings according to some primary visual channel.
What if you wish to make several things easily searchable at the same time?
The solution is to use different channels.
p.33

26. Lesson For Design
For example:
p.33

27. It is not necessary to restrict ourselves to a single channel for each kind of
symbol.
• Differences on multiple channels >> easier to find
p.34

28. p.34

29. Any complex design will contain a number of background colors.
Creating a display containing more than eight to ten independently searchable
symbols is probably impossible simply because there are not enough channels
available.
When we are aiming for pop-out, we only have about three difference steps
available on each channels: three sizes, three orientations, three frequencies of
motion, etc.
p.35

30. Many kinds of visibility enhancements are not symmetric.
• Adding an extra part to a symbol is more distinctive than taking a
part away.
• Increase in size will be more distinctive than a decrease in size
• Increase in contrast will be more distinctive than a decrease in
contrast
p.35

31. Motion
Our sensitivity to static detail falls off very rapidly away from the central
fovea.
Our sensitivity to motion falls off much less, so we can still see that
something is moving out of the corner of our eye, even though the shape is
invisible.
p.36

32. Motion
Motion is extremely powerful in generating an orienting response. Things
that most powerfully elicit the orienting response are not simply things
that move, but things that emerge into the visual field.
p.36

33. Motion
In the design of computer interface, one good use of motion is as a kind of
human interrupt.
• If the motion is rapid, the effect may be irritating and hard to ignore,
and this would be useful for urgent messages.
• If the motion is slower and smoother, the effect can be a gentler
reminder that there is something needing attention.
Signaling icons should emerge then disappear every few seconds or minutes
to reduce habituation.
The gratuitous use of motion is one of the worst forms of visual pollution, but
carefully applied motion can be a useful technique.
p.36

34. Visual Search Strategies and Skills
At every instant in time part of the brain is planning the next eye movement
based on
• information available from the current fixation of the eye.
• some small amount that is retained from the previous few fixations.
• Previous experience
• Influence the visual search pattern
• Where skill comes in
Graphic design:
• Visual structure at several scales can aid search process
• Large-scale structure is needed as a means for finding important mid-
scale and small-scale information.
p.37

35. The Detection Field
The area around the center of the fovea where the presence of a particular
target may be detected can be thought of as a detection field.
In the absence of a candidate target in the detection field, the purpose of a
scanning strategy is to get the eye in the vicinity of the target so that the
feature-based pop-out mechanism can function as a final step.
p.38

36. If small target patterns are embedded in specific types of large patterns, then
this information can be used.
First we make an eye movement to the likely neighborhood of a target, based
on the limited information in our peripheral vision; next, the local pattern
information provides a few candidates for individual detailed fixations.
p.39

37. Inhibition of Return
• Avoid revisiting places that have already been examined.
• Without a blocking mechanism the eye would be trapped, flicking back
and forth between the two most likely target areas.
• It is thought that a structure on the where pathway called the lateral
interparietal area performs this function.
• Experimental evidence suggests that between four and six locations
recently visited with eye movements are retained.
p.39

38. The visual Search Process
• Move and scan loop
• Eye movement control loop
• Pattern-testing loops.
p.40

39. Using Multiscale Structure to Design For Search
Having structure at multiple scales is most important for designs that will be
used over and over again. But even for designs that are used only for a few
minutes, high-level structure supports location memory and makes it easier
to revisit places that have been looked at only seconds ago.
p.40-41

40. Conclusion
p.41

41. One key to making efficient visual search is through the use of pop-out
properties. If a visual object is distinct on one or more of the visual channels,
then it can be processed to direct an eye movement.
The strongest pop-out differentiators are the basic feature channels found in
V1.
Large-scale graphic structure can also help with visual search, but only if the
searcher already knows where in a large structure an important detail exists.
p.42